The Metabolism Core is a state-of-the art facility for assessing human energy expenditure, body composition, and risk for chronic metabolic disease. It provides expertise, resources, and training in: ? Energy expenditure (free-living energy expenditure by doubly-labeled water and isotope-ratio mass spectrometry); ? Body composition and fat distribution [(underwater weighing and BodPod for measurement of whole body density; dual-energy X-ray absorptiometry (DXA) for measurement of regional and whole-body bone, fat, and soft lean tissue; isotope dilution for assessment of total body water; multi-compartment models of body composition; analysis of regional body composition (intra-abdominal and subcutaneous abdominal adipose tissue from computed tomography scans)]; ? Insulin sensitivity testing (frequently-sampled, intravenous, glucose tolerance test with minimal modeling); oral glucose tolerance test with analysis of insulin and glucose; ? Analysis of glucose, lipids, and hormones (including obesity-related hormones, e.g., leptin, adiponectin; diabetes-related hormones, e.g., insulin, C-peptide, glucagon, GLP-1, GIP; a reproductive-endocrine panel, e.g., estradiol, testosterone, other steroid hormones, gonadotropins; elements of the IGF system, e.g., IGF-1 and its binding proteins; cytokines and markers of inflammation, e.g., TNF-a and its receptors, IL-6, CRP); ? Analysis of isotopically-labeled glucose and amino acids by GC/MS for use in in vivo metabolic studies (e.g., endogenous glucose production, protein turnover). Since inception in 2000, Core A has supported 65 investigators and 102 research projects. Current core use includes 24 investigators from 13 departments/divisions across DAB, and seven investigators from outside of DAB. These investigators have a total of 47 funded projects that use Core services. Of these projects, 38 (81%) are federally-funded. Two CNRU P/F studies presently use the Metabolism Core. New Methods Development includes, 1) the validation of a non-invasive test for insulin sensitivity in children using a mixed-meal, and, 2) implementation of methodology for assessing insulin secretion and clearance using data resulting from a mixed-meal test.